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As the Pentagon announced it was un-grounding the F-35 fleet following an investigation into a June engine fire, the commandant of the Marine Corps reiterated his support for the fighter program and said the mishap amounted to a fluke.

“This is what we would probably call a one-off,” said Gen. Jim Amos, speaking at an event hosted by the Brookings Institution on Tuesday. “It doesn’t mean it’s not significant; it doesn’t mean we’re not going to pay attention to it. But it does mean that the level of confidence to return to flight operations is pretty doggone high.”

The entire F-35 fleet was grounded July 3 following an F-35A fire at Eglin Air Force Base, Florida, on June 23. Pentagon acquisitions chief Frank Kendall told reporters in London 10 days later that the fire was caused by “excessive rubbing” of fan blades inside the plane’s engine, though it wasn’t immediately clear what led to the problem.

Officials announced Tuesday morning that all F-35s were cleared for flight, with some limitations.

Amos said that 95 or 96 F-35 engines were inspected. As of Monday night, all but three were cleared, he said, but it still wasn’t clear why the fan blade rubbing caused the engine to catch fire.

“This is called developmental testing,” he said. “There’s a reason it has that name. Everything, whether it be the Ford Pinto or whether it be the F-35B, went through developmental testing and they found things.”

This grounding is the second for the costly new fighter fleet. In February, officials discovered a crack in the engine of a Marine F-35B, and grounded all F-35s for a week while the problem was investigated.

The Marines’ version of the plane, the F-35B Joint Strike Fighter, is expected to reach initial operating capability late next summer. Amos said the recent grounding had not affected that timeline.